Rhizobacteria from Rhizosphere of Sunflower ( Helianthus annuus L.) and their effect on Plant Growth

Rhizosphere harbors a vast population of bacteria; among them a beneficial group is the Plant Growth Promoting Rhizobacteria (PGPR) that help plant growth promotion. Sunflower is an important oilfield crop and has also been used in bioremediation and phytoremediation studies. Several of these bacteria were isolated from different sites, the bulk soil, rhizosphere and endorhizosphere regions of this experimental plant and their effects on plant growth were studied. The stimulation of plant growth is attributed to various plant growth promoting mechanisms. Study of the direct mechanisms i.e. production of phytohormones, solubilization of Phosphate and the indirect mechanisms- antifungal activity against plant pathogenic fungi, production of lytic and detoxification enzymes, Siderophore production, production of Ammonia and HCN were also carried out. Among the isolates, about 30 rhizobacteria that were positive for several of these plant growth promoting mechanisms were selected for plate germination and pot assay experiments. The bacteria mainly belonged to the Azotobacter , Pseudomonads, and the Bacillus group. From the plate experiments seven of the bacteria were selected i.e. four rhizosphere isolates, one endorhizosphere isolate and two soil isolates gave promising results when compared to control. All of the isolates also showed elongation of roots. Three had elongated shoots as compared to control in pot trial experiments. These isolates will be further tested for field experiments.